Radioactive source terms are important factor in design, licensing and operation of SMR (Small Modular Reactor). In this study, regulatory requirements and evaluation methodology for normal operation on NuScale SMR, which received standard design certification approval on September 11, 2020 from US NRC, are reviewed. The radioactive waste management system of nuclear power reactor should be designed to limit radionuclide concentration in effluents and keep radioactive effluents at restricted area boundary ALARA according to 10 CFR 20 and 10 CFR 50 Appendix I. Also, in general, the coolant source term to calculate the off-site radiological consequences for normal operation of SMR should be determined by using models and parameters that are consistent with regulatory guide 1.112, NUREG- 0017 and the guidance provided in ANSI/ANS-18.1-1999, and the result should be corrected by reflecting the design characteristics of SMR. The coolant source term of NuScale, unlike the case of large NPPs, cannot rely solely on empirical source term data, because the NuScale source term is based on first principle physics, operational experience from recent industry, and lessons learned from large PWR operation. Fission products in reactor coolant are conservatively calculated using first principle physics in SCALE Code assuming 60 GWD/MTU. The release of fission products from fuel to primary coolant based on industry operational experience is determined as fuel failure fraction of 0.0066% for normal operation source term and 0.066% for design basis source term while coolant source term of large NPP is calculated by using ANSI/ANS-18.1 for normal operation and fuel failure fraction of 1% for design basis source term. Water activation products in reactor coolant are calculated from first principles physics and corrosion activation products are calculated by utilizing current large PWR operating data (ANSI/ANS 18.1- 1999) and adjusted to NuScale plant parameters. Also, because ANSI/ANS 18.1-1999 is not based on first principle physics models for CRUD generation, buildup, transport, plate-out, or solubility, NuScale has incorporated lessons learned by using ERPI’s primary water chemistry and steam generator guidelines to ensure source term is conservative and design of materials used cobalt reduction philosophy to help ensure the coolant source term are conservative. Based on the coolant source term calculated according to the above-described method, the annual releases of radioactive materials in gaseous and liquid effluents from NuScale reactor are evaluated. Currently, Small Modular Reactors such as ARA, SMART 100 are under review for licensing in Korea. This study will be helpful to understand how the reactor coolant system source terms are defined and evaluated for SMR.

Recently, about 70 Small Modular Reactors (SMRs) are being developed around the world due to various advantages such as modularization, flexibility, and miniaturization. An innovative SMR (i- SMR) is being developed in South Korea as well, and the domestic nuclear utility is planning to apply for the Standard Design Approval in 2026 after completing the basic design and standard design. Accordingly, the regulatory body is conducting research on the regulatory system for reviewing the i- SMR standard designs by referring to the IAEA and the U.S. NRC cases. A SMR is expected to many changes not only in terms of cyber security due to new digital technology, remote monitoring, and automatic operation, but also in terms of physical security according to security systems, security areas, and vital equipment. Accordingly, related technical documents issued by the IAEA require nuclear utilities to consider regulatory requirements of security from the design phase by integrating security regulations into SMR licensing. The U.S. NRC has also identified 17 issues affecting SMR design since 2010 (SECY-10-0034), and among them, ‘Consideration of SMR security requirements’ was included as a major issue. Accordingly, the NuScale applicant conducted security assessment and design in consideration of the Design Base Threat (DBT) in the initial SMR design process through the Gap Analysis Report (2012) and the NuScale’s Security System Technical Report (TR-0416-48929), and the NRC developed the Design Specific Review Standard for NuScale (DSRS) and then reviewed the applicant’s security design process, standard design results, and testing criteria for security system (ITAAC). This paper analyzed the case of security review activities during the NuScale standard design review, and through this, it is intended to be used in the development of domestic regulatory system for the i-SMR security review in the future.